Alternating-current motor.



Patented Feb. 6, I900.

W. LANGDUN-DAVIES.

ALTERNATING CURRENT MDTOR.

(Application filed. May 22, 1899.)

5 Sheets$heet I.

(No Model.)

Patehted Feb. 6, I900.

W. LANGDON-DAWES.

ALTERNATING CURRENT MOTOR.

(Application filed. HA)! 22, 1899.)

5 Shuts-Shoat 2.

(No Model.)

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No. 643,066. Patented Feb. 6, 1900. w. LANGDON-DAVIES.

' ALTEBNATING CURRENT MOTOR.

(Application filed. May 22, 1899.)

(No Model.) 5 Sheets-Sheet 3.

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No. 643,066. Patented Feb. 6, I900. W. LANGDON-DAVIES. ALTEBNATINGCURRENT MBTOB.

(App ication filed May 22, 1899.) (No Model.) 7 5 Sheets-Sheet 4.

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N0. 643,066. Patented Feb. 6, I900. W. LANGDUN-DAVIES.

ALTERNATING CURRENT MOTOR.

(Application filed. May 22, 1899.)

(No Model.)

5 Sheats$heet 5.

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UNITED STATES PATENT OEEIcE.

WALTER LANGDON-DAVIES, OF LONDON, ENGLAND, ASSIGNOR TO THELANGDON-DAVIES ELECTRIC MOTOR COMPANY, LIMITED, OF SAME PLACE.

SPECIFICATION forming part of Letters Patent No. 643,066, dated.February 6, 1900. Application filed May 22, 1899. Serial No. 717,810.(NomOdeL) To to 1071,0111, it 77211.7 concern:

Be it known that I,WALTEE LANGDON-DA- vIEs, electrical engineer, asubject of the Queen of Great Britian, residing at 101 Southwark street,London, in the county of Surrey, England, have invented certain new anduseful Improvements in Alternating-Current Motors, of which thefollowing is a specification.

The object of my invention is to produce an alternating-current motorfrom which a large starting effort can be obtained and the speed ofwhich can be continuously regulated electrically and is not entirelydependent on the periodicity of the current.

My improvements are illustrated in the drawings annexed.

Figure 1 is an end elevation of a motor of the class to which myimprovements apply. Fig. 2 is an end view of a ring-armature without anywinding. Fig. 3 is a diagram end View of a motor constructed accordingto my invention. Figs. 4, 5, and 6 are similar diagrammatic viewsillustrating the effect of three different distributions of thefield-windings. Fig. 7 is a diagram View showing how a magnetic fieldsimilar to that shown in Fig. 3 may be produced by-a differentdisposition of the field-windings to that shown in that figure. Fig. 8is a diagram View of a motor such as shown at Fig. 3, but provided withtwo sets of field-windings, one to be used for running in one directionand the other in the other direction. In Fig. 8 the outer windings onlywhich pass through the end slots in each pole-face are seen. In Fig. 3these windings are somewhat bent aside, so that portions of the windingpassing through the other slots may be seen.

The motor has two elements-one fixed, which I call the field-magnet, andone rotating, which I call the armature. Each element is wound withcoils. The coils on one element are energized by the supply-current andinduce current in the coils on the other element. When the coils on thefieldmagnet are energized by the supply-current, the armature is woundwith coils in which currents are induced by the field-magnet, the coilsare connected to a suitable commutator,

to the mains; b, the armature; c, commutatorbars, to which thearmature-winding is coupled at intervals, and d d brushes connected toone another. The arrow 1 indicates the magnetic axis of thefield-magnets, (it is shown as being horizontal,) and the arrow 2 themagnetic axis of the armature. It is in a line with the points ofcontact of the brushes. If the axes of the fields in the field-magnetand armature do not coincide, the field of the fieldmagnet and the fieldof the armature will repel one another, and a continuous rotation willresult.

Motors on the general principles above de scribed have been made, butare inefficient.

In such an arrangement as that shown in Fig. 1 the reluctance in thepath of a field having its axis on the line shown by the arrow 2 isgreater than that of a field having its axis on the line shown by thearrow 1. There fore one of the fields would be weaker than would be thecase if reluctance was the same for each field, and as the power isderived from the reaction of these two fields upon one another therewould be less power obtainable, and therefore an arrangement such asshown in Fig. 1 must necessarily be very imperfect.

In motors working upon the above general principle I according to myinvention wind the field on a continuous ring of iron having noprojecting pole-pieces and suitably laminated and provided with slots orholes to receive the windings, as shown in Fig. 2, and for the reasonshereinafter stated I also so dispose the windings as to make themagnetic density uniform over or strongest at the center of eachpole-face. It may be assumed in such a machine of fixed dimensions ashas through each slot.

been described that the torque or turning effort with a given strengthof ind ucing-field is proportional to the amount of current flowing inthe induced windings, provided the brushes are fixed in position. I findthat the amount of current induced in the induced windings by a giventotal strength of inducing-field may vary considerably with the way inwhich the inducing-field is distributed over the pole-faces and that thebest results are obtained by so distributing the field-windings as tomake the magnetic density strongest in the center of the pole-face anddecreasing at the outer edges, as indicated by Fig. 3, in which thedotted lines represent, diagrammatically, the lines of force. To producethis result, I may wind my inducing-field in sec tions, so that the ironis surrounded by different numbers of turns, which increase the magneticdensity toward the center of each pole-face. The field-windin g requiredto produce such a field will vary more or less for different sizes andvaried forms of the motor;

' but generally to produce such a magnetic field one turn of thefield-winding may, for example, be passed through slots marked No. 1 inFig. 3 and be available for more or less magnetizing the whole of theiron in the space between these slots. Another turn of the winding maybe carried through the slots No. 2 and be available for increasing themagnetization of the iron in the space between them, and so on to theslots No. 8, near the center of the pole-face. The induction density canthen be tested by means of an exploring-coil in the known way, or thearmature itself may be used as the exploring-coil and the voltagefordifferent positions of the brushes be taken. The information soobtained will indicate what corrections have to be made in theproportioning of the field-windings to produce the field required.

To illustrate the eifect of different forms of winding, I have in thediagrams Figs. 4, 5, and 6 illustrated approximately the electrical andmagnetic conditions produced by Various forms of winding. In Fig. 4 themagnetic density is shown as being greater toward the ends of eachpole-face than at the center. In Fig. 5 the density is uniform, orapproximately so, over the pole-face, (directions for so proportioningthe windings as to produce a uniform magnetic density are given in thespecification of a former patent, issued to me May 17, 1898, No.604,055,) and in Fig. 6 it is greater at the center than at the ends,and this is effected by passing a greater number of turns of windingthrough the slots which are near the center of the pole-face than wouldbe required to produce uniform density, as in Fig. 5. Approximately itis desirable in most cases that an equal number of turns or windingsshould be passed The figures diagrammatically represent a two-polemotor. In each of the figures, a is a field-magnet ring. b is thearmature, having sixteen teeth. The armature is shown wound with acontinuous ring-winding having one turn wound in each notch between theteeth. This winding is shown connected in the usual manner to asixteen-part commutator c. The dotted lines from the field-magnetthrough the armature and back to the field-magnet represent the magneticfield. The different numbers of lines entering each tooth of thearmature are intended to graphically represent the density of themagnetic field over the pole-faces. The whole upper half of the insideface of the field-magnet is considered as one poleface and the lowerhalf as the other pole-face. There is no gap in the iron between them.In other words, these are not what are to be understood as projectingpoles. It is assumed in the following deductions that one magnetic lineof force alternating in one turn of the armature-winding produces apotential ditference of one volt at the terminals of that turn-that isto say, in the winding shown, having one turn between eachcommutator-segment, the volts between each pair of commutator-segmentsare equal to the number of magnetic lines alternating through the turnof winding between them. The volts between the pairs ofcommutator-segments are written above the commutator in each of thefigures, and the directions of the arrows show the relative directionsin which current would flow. In each of the figures the same totalnumber of magnetic lines is assumed to be produced by the field-magnetand to pass through the armature. By adding the volts between thesectors, giving them their positive or negative values, as shown by thedirection of the arrows, the volts between a pair of brushes placed atthe ends of any diameter of the commutator can be calculated. Themaximum volts obtainable in Fig. 4 are forty-four, in Fig. 5 sixty-four,and in Fig. 6 eighty-four. As the only difference in the construction ofthe three figures consists of the diiferent distribution of the inducingmagnetic field it is obvious that the greatest induced current, andtherefore torque, can be obtained from the arrangement shown in Fig. 6.A practically similar magnetic field having the lines of forceconcentrated to the central portion of each pole-face can, as shown atFig. 7, be produced by winding the central portion only of the pole-facewith a single coil. In such a case it will not be necessary to wind theinducing-coils in sections, but, as shown, the central portion only, notexceeding or much exceeding one-half of the poleface, may be Wound witha single coil.

The magnetic distribution obtained by such a field-magnet as that shownin Fig. 1 may effectively resemble that shown in Fig. 7; but owing tothe gaps in the magnetic circuit the gain by distribution will have tobe set off against the losses arising from the reluctance of the path ofthe field set up by the induced current.

If the armature-windings are connected to IIO the source of supply bymeans of the brushes, the distribution of the field set up by thearmature will be similar to the inducing-field shown in Fig. 6, sincethe armature-windings are distributed over the pole-face, though theposition of its axis will depend on the position of the brushes. Henceit is apparent that to produce the same results the same constructionmust be used, whether the fixed or rotating part, or both of them, beenergized by the supply-current.

The proportions of turns in the sections and the most suitabledistribution for the field may, as above stated, be found by experimentand will vary for different sizes of motors and for the different kindsof work they are required to perform; but the field should always bebanked to the center, as in Figs. 6 and 7, by means of the winding andwithout projecting poles.

Although I have only shown my improvements applied to a two-polemachine, it is evident that they may be applied to machines having agreater number of poles.

The motor may be controlled as to speed and power by introducing chokeor resistance into the induced or inducing winding, either or both.

To change the direction of rotation of such a motor, I in some caseswind the field magnet ring, as illustrated at Fig. 8, with two sets ofwindings e f, set at an angle to one another such that the axis of thefield produced by one set of windings 6 lies at a suitable angle to theaxis of the other or armature-field to produce rotation in one directionand the field set up by the other field-windingf produces a rotation inthe opposite direction. The magnetic field produced by the winding f isindicated by the dotted lines. In this way the direction of rotation canbe controlled by a suitable switch exterior to the motor bringing intoaction one or the other set of windiugs, as required.

What I claim is 1. An alternating-current motor having its field-magnetsformed in a drum-wound slotted continuous ring with no projectingpolepieces and their windings so distributed as to make the magneticdensity strongest at the center of each pole-face and having itsarmature wound with a continuous winding coupled at intervals tocommutator-bars and also having brushes bearing against the commutatoron a line inclined to the magnetic axis of the field-magnets and inwhich the circuit through the field-magnet windings and the circuitthrough the armature-windings and brushes are the one supplied withcurrent and the other short-circuited.

2. An alternating-current motor having its field-magnets formed in adrum-wound continuous ring with no projecting pole-pieces and having thecentral portion only not exceeding or much exceeding one-half of eachpole-face embraced by the field-windings and having itsarmature-windings coupled at intervals to the bars of a commutator andbrushes bearing against the commutator on a line inclined to themagnetic axis of the field-magnets and in which the circuit through thefield magnet windings and the circuit through the armature-windings andbrushes are the one supplied with current and the other short-circuited.

3. An alternating-current motor having armature-windings coupled atintervals to comm utator-bars and brushes bearing on the commutator andhaving its field-magnets formed in a drum-wound slotted continous ringhaving no projecting pole-pieces and provided with two sets of windingsone to be used when the motor is to run in one direction and the otherwhen it is to run in the opposite direction.

WALTER LANGDON-DAVIES.

\Vitnesses:

ROBERT E. RANSFORD, JOHN H. WHITEHEAD.

